so none were hacked or modded characters?
I mean none of the characters were characters that transform/switch or anything. All of these characters work fine also (even transforming/switching ones), its just crashing with 4 human players specifically, no matter what characters are selected.
I used to have that kind of problem in riivolution to, (but I use gecko now) it must be the common5_en.pac being compressed wrong by pressing save in brawbox (older or new) which messes up the file and the select screen. But when pressing save as, it worked perfectly for me. So it might be that or the wrong file you downloaded.
I'm busy during this week, so I'll try messing around with the common_5 over the weekend